A known oil supply device for a vehicle, disclosed in JP2004-116430A (hereinafter referred to as Reference 1) includes a mechanical oil pump, an electric oil pump, a first relief valve, and a second relief valve. A discharge port of the mechanical oil pump and a suction port of the electric oil pump are connected in series with each other. The first relief valve opens when a pressure of the discharge port of the mechanical oil pump is higher than a first predetermined pressure. The second relief valve is arranged between a discharge port of the electric oil pump and an oil jet device (hydraulic actuator). The second relief valve opens when a pressure of the discharge port of the electric pump is higher than a second predetermined pressure. The discharge port of the mechanical oil pump connects to a lubricating route (engine lubricating system) that supplies a lubricating oil to portions of an internal combustion engine. In addition, the discharge port of the electrical oil pump connects to a variable valve timing device. The second predetermined pressure is set at a value larger than a value of the first predetermined pressure.
According to the oil supply device disclosed in Reference 1, the electric oil pump is arranged so as to be connected to the mechanical oil pump in series therewith while serving as a supplementary pump for the mechanical oil pump; therefore, an insufficient hydraulic pressure due to the mechanical oil pump may be compensated by the electric oil pump. However, the electric oil pump is applied to the oil supply device so as to serve only as the supplementary pump, therefore increasing a whole size of the oil supply device and leading to an increase of the weight and cost. Additionally, a more space to which the oil supply device is attached is required.
A need thus exists for an oil supply device, which is not susceptible to the drawback mentioned above.